OBJECTIVE： To study the stability of Tramadol hydrochloride， Fentanyl citrate and Ondansetron hydrochloride injection in 0.9％ Sodium chloride injection. METHODS： At room temperature [（25±1） ℃]， three injections were poured into infusion bag of disposable analgesia pump， and diluted with 0.9％ Sodium chloride injection. The changes in precipitation， turbidity， color and pH value of the mixture were observed. The relative percentage of three injections within 72 h were determined by HPLC method. RESULTS： There was no significant change in the pH value and appearance of the mixture. Relative percentage of tramadol hydrochloride， fentanyl citrate and ondansetron hydrochloride were all higher than 97％ within 72 h. CONCLUSIONS： The mixture of Tramadol hydrochloride， Fentanyl citrate and Ondansetron hydrochloride injection in 0.9％ Sodium chloride injection keep stable within 72 h under room temperature.